The present disclosure relates to compounds, e.g., multisubstituted aromatic compounds, which exhibit biological activity, e.g., inhibitory action, against thrombin (activated blood-coagulation factor II; EC 3.4.21.5).
In mammalian systems, blood vessel injuries result in bleeding events, which are dealt with by the blood coagulation cascade. The cascade includes the Extrinsic and Intrinsic pathways, involving the activation of at least 13 interconnected factors and a variety of co-factors and other regulatory proteins. Upon vascular injury, plasma factor VII interacts with exposed Tissue Factor (TF), and the resultant TF-fVIIa complex initiates a complex series of events. Factor fXa is produced directly ‘downstream’ from the TF-fVIIa complex, and amplified manifold via the Intrinsic Pathway. FXa then serves as the catalyst for formation of thrombin (fIIa), which in turn is the direct precursor to fibrinolysis. The outcome is a fibrinolytic clot, which stops the bleeding. Fibrinolysis of the polymeric clot into fibrin monomers leads to dissolution and a return of the system to the pre-clot state. The cascade is a complex balance of factors and co-factors and is tightly regulated.
In disease states, undesired up- or down-regulation of any factor leads to conditions such as bleeding or thrombosis. Historically, anticoagulants have been used in patients at risk of suffering from thrombotic complications, such as angina, stroke and heart attack. Warfarin has enjoyed dominance as a first-in-line anticoagulant therapeutic. Developed in the 1940s, it is a Vitamin K antagonist and inhibits factors II, VII, IX and X, amongst others. It is administered orally, but its ease of use is tempered by other effects: it has a very long half life (>2 days) and has serious drug-drug interactions. Importantly, since Vitamin K is a ubiquitous cofactor within the coagulation cascade, antagonism results in the simultaneous inhibition of many clotting factors and thus can lead to significant bleeding complications.
Much attention has been focused on heparin, the naturally-occurring polysaccharide that activates AT III, the endogenous inhibitor of many of the factors in the coagulation cascade. The need for parenteral administration for the heparin-derived therapeutics, and the inconvenient requirements for close supervision for the orally available warfarin, has resulted in a drive to discover and develop orally available drugs with wide therapeutic windows for safety and efficacy.
Indeed, the position of thrombin in the coagulation cascade has made it a popular target for drug discovery. Thrombin is a central protein in the coagulation process, which is activated and amplified upon vascular injury. Thrombin generation prompts a cascade in various factors in the coagulation cascade, ultimately depositing fibrin, the framework for a clot. The clot causes cessation of the bleeding event accompanying the vascular injury.
Thrombin and associated protein ultimately cause dissolution of the clot through ‘fibrinolysis’, returning the system back to the pre-injury state. In a ‘normal’ state of injury, this thrombin generation and clot deposition is desired. In a disease state, clot deposition is undesired. General thrombotic events are the clinical result of clot deposition and accumulation in the arteries, veins or within the heart. Eventual break-off of the accumulated clot structure into the vascular system can cause the clot to travel to the brain and/or lungs, resulting in a stroke, myocardial infarction (heart attack), pulmonary embolism, paralysis and consequent death. Compounds that inhibit thrombin have been shown in the literature to be useful as anticoagulants in vitro and in vivo, and such compounds can fulfill a critically unmet medical need for patients in the clinic.
A thorough discussion of thrombin and its roles in the coagulation process can be found in a variety of references, including the following which are incorporated herein by reference in their entireties and for all purposes: Wieland, H. A., et al., 2003, Curr Opin Investig Drugs, 4:264-71; Gross, P. L. & Weitz, J. I., 2008, Arterioscler Thromb Vasc Biol, 28:380-6; Hirsh, J., et al., 2005, Blood, 105:453-63; Prezelj, A., et al., 2007, Curr Pharm Des, 13:287-312. Without wishing to be bound by any theory, it is believed that the ultimate development of direct thrombin inhibitors (DTIs) is usefully based upon the classical D-Phe-Pro-Arg motif, a sequence that mimics fibrinogen, which is a natural substrate of thrombin. Without further wishing to be bound by any theory, it is believed that the use of DTIs is very well precedented, such as with the hirudin-based anticoagulants, and thus there is strong interest in the discovery and development of novel DTIs, particularly those with selectivity for inhibiting thrombin over other related serine proteases.